Electron discharge device comprising auxiliary electrode in grid section



ELECTRON DISCHARGE DEVICE COMPRISING AUXILIARY ELECTRODE IN GRID SECTION Filed Sept. 28, 1962 Sept. 27, 1966 M E. ULUG 3,275,876

UUUUUUUUUUUUUUIIWWUU 0) MEHMET E. ULUG BY Y. f y' gf f) I,

United States Patent O 3,275,876 ELECTRON DISCHARGE DEVICE COMPRISING AUXILIARY ELECTRODE IN GRID SECTION Mehmet Esin Ulug, Etobicoke, Ontario, Canada, assignor to Canadian General Electric Company, Limited, To-

ronto, Ontario, Canada, a corporation of Canada Filed Sept. 28, 1962, Ser. No. 226,997 6 Claims. (Cl. 313-238) This invention relates to electron discharge devices and more particularly to the improvement of positive grid number three current characteristics in duel control twin pentodes and dual control twin heptodes.

A dual control twin pentode, tube type GBUS is discussed in an article entitled, A New Noise-Gated Automatic Gain Control and Sync System for Television Receivers-Part II, by George C. Wood published in the IRE Transactions on Broadcast and Television Receivers, dated June 1960, pages 32-34. My invention will be discussed in connection with the above-mentioned tube. A tube using my invention has been registered as a 6|BU8A tube. However, the scope of my invention is not limited to this type only. The construction of the 6BU8 tube is unique in that the cathode, grid number one, and grid number two are common to both pentodes. I'he pla-te and grid number three yare split in lhalf forming two individual plates or sections.

One function of the grid number three of the pentode is to provide a grid leak bias which increases in proportion to the magnitude of the signal voltage between the grid number three and lthe cathode. The grid leak bias is obtained through diode action of the grid number three as the positive lswing of the applied signal tends to drive grid number three into the grid current region.

When the 6BU8 type pentode tube is connected in a circuit and is subjected to very strong signals entering the positive grid region the tube exhibits a defect known as blocking and -it causes saturation or reversal of grid number three current in the positive voltage region as will be shown in association with the description of FIGURE l3. The defect blocking is caused by either the secondary emission of electrons fromV grid lateral wires or by the'potential differences between grid number three and the space charge surrounding it.

Methods to overcome these defects have been employed in the art, such as carbonizing the grid number three laterals, or connecting a grounded electrode (a shield) .to the cathode and 'locating the grounded electrode between grids number two -and three, `to increase the screen grid dissipation. Neither of these methods have proved completely satisfactory and actually have introduced other objectional disadvantages.

I have found that these disadvantages mentioned above can be overcome by providing an -auxiliary electrode in association with one section of .grid number three located in close proximity to the cathode and disposed midway between grid number one and grid number two. 'Ihe electrode forms -a triode having grid number one as =a control grid and a cathode in common -wi-th the pentode section. The grid number one is wound with a variable pitch having the turns of one pitch vadjacent the auxiliary electrode and the turns of another pitch -along the remaining length of the grid. The triode conducts when the grid number three, Ato which the electrode is galvanically connected, is positive. When a noise signal or a negative potential appears on grid number one (the control grid), the triode cuts oil".

The auxiliary electrode connected to grid number three functions as the plate of a triode when the grid number three is positive to provide a grid leak bias current for grid number three so that grid number three does not ex- ICC hibit a reversal ,of current in the positive grid region or premature saturation characteristics. The auxiliary electrode `also provides a rapid adjustment of the grid leak bias voltage in response to an increase in the potential -of the applied signal.

The positive grid number three current characteristics are improved with my invention Without upsetting the negative grid number three characteristics or the noise immunity `action of grid number one.

The negative grid number three characteristics are the characteristics displayed by the grid number three under normal operation with negative grid leak bias.

The noise immunity action of grid number one means that grid number one will prevent the electrons from flowing to -both plates if a noise signal or a negative signal is applied to it.

The characteristic features of the invention are defined in the appended claims and one embodiment is -described in the following specification and shown in the accompanying drawings vin which:

FIG. l is a top view of a -tube type 6BU8A using my invent-ion;

FIG. 2 is a sectional view of the same tube taken on the line A-A of FIG. 1; land FIG. 3 is a graph showing the positive gridnumber three characteristics -of 6BU8A and 6'BU8 tube types.

Referring now to FIG. l and FIG. 2 which illustrate a 6BU8A type pentode tube Withou-t a base, contact prongs and an envelope which have been omitted, the part between the upper vtop mount 8 and bottom mount 9 being shown. An anode plate |10 is shown in FIG. l (omitted in FIG. 2) which partially surrounds grid num- -ber ythree (6), a screen grid number two (5), a gri-d number one (3) Iof which a side rod 7 is shown in FIG. 2, and a cathode 1 which is coated on a cathode sleeve 2. A shield '11 en-closes the cathode '1, grid '3 and grid 5. The plate -10 and the grid 6 are split in half, eac-h forming two individual sections. The cathode -1 emits an electron stream which can go in two separate directions and after traversing grid 3 and screen grid 5 may pass -through grids 6 to each of the sections of plates 10 providing none tof the grids are biased -beyond cutoff. My invention comprises an auxiliary electrode 4 which may be termed a triode plate and which is illustrated as being galvanically connected, that is, conductively connected, to one section of the grid 6 in the 4tube and disposed midway between the grid 3 and the screen grid 5. The section of grid 6 connected to the auxiliary electr-ode 4 becomes the plate of a triode which has a cathode 1 and control grid thatis actually part of grid 3. The part of lgrid 3 which acts as the control grid -of the triode is wound with a pitch which is different from the pitch of the remainder of grid y3 in common with the pentode.

This triode conducts Without saturation when the grid 6 is positive and cuts off completely when a noise signal lappears on grid The electrode 4, being galvanically connected to lthe grid 6 improves the grid leak perform- -ance of grid 6. That is to say, the current characteristic lof grid 6 does not saturate and does not reverse its direction, as will be shown in the description of FIG. 3.

The electrode 4 of FIG. l and FIG. 2 is shown in the form of a small metallic plate-like tab located at the top of a mount 8 in close proximity to the cathode 1. The area of the electrode 4 should be of such dimensions that it provides a grid leak bias through diode action of the grid 6 as the positive swing of the applied signal tends to drive grid 6 into grid current region.

In a 6BU8A type dual control twinpentode tube used in a sync separator-clipper and automatic gain control circuit for a television receiver, I have found that a small metallic tab 0.060 inch wide, 2 mm. long, and 0.005 inch y ance at low signal levels.

Vcapabilities of grid number three the lower values of grid thick galvanically connected to the control grid 6 and located approximately 0.045 inch from the cathode center line, as shown in FIG. l and FIG. 2 operates very'effectively to overcome the difiiculty of slow acting grid biasing of other dual control twin pentode tubes, i.e. the 6BU8 tube. In addition the cathode coating has been extended 1 mm. at the top of mount 8 and seven turns of wire have been removed from grid 5 to provide a triode tube in association with the pentode section. Also, the grid Shas been `wound with a 60 turns per inch pitch adjacent The characteristic current does not saturate or reverse its direction for the voltage range of 1-60 volts. Curve 211represents the positive characteristics of the number three grid of a 6BU8 tube. The region A in the curve 21 is a positive grid region and extends normally to a value of about 5 volts. The current saturates around 400 microamps and has a knee at 5 volts. The region B extends from` plus 5 volts to about 50 volts and the Lregion C extends from about 50 volts to full plate voltage.. Referring to thel curves it will be noted that the region B on curve 21 shows a negative slope. This negative resistance or slope is one reason for the difficulty known as blocking` and when blocking occurs the grid is thrown into region B. Once this region B is entered, the grid potential remains in the bottom of the valley indicated on curve 21 between regions B and C. It happens that the grid potential in this region is approximatelyrSO volts and is positive and the grid will remain .at a high positive value for a period of time since the amplitude' of the currentdrawn by the number three grid is not enough -to charge up a grid leak condenser and restore negative bias. At this high positive grid number three voltage the plate `current is only limited by the emission from the cathode and this high current is sufficient to overheat the tube,

liberate gas, and destroy the function of the tube, nally causing the destruction of the tube.

It will be apparent from the curve 20 shown that blocking will not occur in the 6BU8A tube since the current at 50 volts is around one milliamp and the value of the grid number three current is much larger than usual emission currents from 'the grid laterals. A 6BU8A type dual control twin pentode will also have the advantage of reducing the grid leak bias resistance required, by a considerableamount without deterioratingV the tubes perform- Because of the higher current leak bias resistance will help to provide long and Vtroublef ymounted in `spaced position, first, second, and third con` trol grids'mounted in a spaced sequence fromthe cathode Vto the anode; and an auxiliary electrode conductively con` nec-ted to said'third control grid and` positioned in kclose proximity to the cathode to improve the positive voltage characteristics for said third control grid.

2. An electron discharge device comprising-a. substantially evacuated envelope enclosing a cathode and an anode mounted in spaced position, first, second, and third control grids mounted in a spaced sequence from the cathode to the anode; `and `an auxiliary electrode conductively connected to said third control grid and positioned between said first and second control grids.

3. An electron discharge device comprising, a substan-` tially evacuated envelope enclosing a cathode and an anode mounted in spaced position, first, second, and third control gridsA mounted in a spaced sequence from the cathode to the anode; and an auxiliary electrode conductively connected to said third control grid, said auxiliary electrode comprising a short metallic :plate-like Itab'extending on one side only of said third control grid and positioned halfway between said first and second control grids.

4. An electric discharge device comprising, `a substantially evacuated envelope enclosing `a cathode 4and an anode mounted in spaced position, first, second, .and` third control gridsr mounted in a spaced sequenceV from the cathode to the anode, said first grid being Wound with a.

variable pitch, and an auxiliary electrode conductively connected to said third control grid, said auxiliary electrode comprising a small metallic plate-liketab positioned adjacent toy one side of said third control grid andhalfway between said first and second control grids, said first control grid having a different pitch adjacent said auxiliary electrode than the pitch for the remainder of the first control grid. Y

5; A dual control twin pentode tube comprising ytwo pentode sections, a substantially evacuatedenvelope en?. closing a cathode and an anode in each section, said cath-` ode being common to both of the pentode sections of said tube; first and secondcontrol grids being common 1 to both of the pentode sectionsof said tube, said first grid being wound with a variable pitch; a pair ofk third `control grids, one in each pentode section being separated Yfrom said first and second control grids and positioned between said second grid and the anode in" each section, an auxiliary electrodelconductively connected to only one of said` third control grids and positioned midway between said first and second control gridsin one of pentode section.`

6. lA dual control twin pentode ,tube comprising Itwo pentode sections, a substantially evacuated envelope` enclosing a cathode and an anode in each section, said cathode being common to both `of the pentode sections of said tube; first and second` control grids being common to both of the pentode sec-tions of said tube, said first grid being,` wound with a variable pitch; a pair of third control grids,`

one in each `pentode `section being separated from said first' and second control -grids and positioned between said second Jgrid and the anoderin each 'section,an auxiliaryl electrode conductively connected tov only one of said third 'control grids and positioned midway between said first Aand second control grids Vin one yof pentode section, said first control grid havinga different pitch'adjacent saidk auxiliary electrodethan theVpi-tchy for the `remainder of the first control grid.` A

ReferencesA Cited by the Examiner i Y UNITED y.STATES PATENTS 2,03 6,695

J. D KALLAM, Assi'smm Examinar.

4/1936 .Herold 1.--; 31st- 29aV 2,999,985 1. -9/1961 Tongue v 313-299- 

1. AN ELECTRON DISCHARGE DEVICE COMPRISING, A SUBSTANTIALLY EVACUATED ENVELOPE ENCLOSING A CATHODE AND ANODE MOUNTED IN SPACED POSITION, FIRST, SECOND, AND THIRD CONTROL GRIDS MOUNTED IN A SPACED SEQUENCE FROM THE CATHODE TO THE ANODE; AND AN AUXILIARY ELECTRODE CONDUCTIVELY CONNECTED TO SAID THIRD CONTROL GRID AND POSITIONED IN CLOSE PROXIMITY TO THE CATHODE TO IMPROVE THE POSITIVE VOLTAGE CHARACTERISTICS FOR SAID THIRD CONTROL GRID. 